Don't automagically create evdev handlers for autodetection.

Require them to be loaded with -plugin.

This prevents auto-detection (which was not opt-out) from conflicting with the
actual settings on device, which may sometimes cause issues ranging from
useless instantiation to double processing of events which is definitely not
desired.
Merge pull request #9 from rburchell/master

Don't automagically create evdev handlers for autodetection.